The present invention relates to a process for producing N-alkyl pyrazoles which are useful as an intermediate for medicines and agricultural chemicals, in particular, as an intermediate for herbicides.
As for the N-alkylation method for pyrazoles, methods to be described hereinafter have been known.
(1) A method of reacting 4-methylpyrazole and dimethyl sulfate in an aqueous 2N solution of sodium hydroxide is disclosed in Justus Liebigs Annalen der Chemie, 625, 55 (1959). However, the yield of 1,4-dimethylpyrazole in this method is as low as 56%.
(2) A method of reacting 3(5)-methylpyrazole and methyl iodide in the presence of sodium methoxide in a methanol solution to obtain 1,3-dimethylpyrazole and 1,5-dimethylpyrazole is disclosed in Chemisch Berichte, 59, 1282 (1926). However, no satisfactory results are obtainable by this method (refer to Comparative Examples 1 and 2 to be described later).
It has strongly be demanded for providing a process for producing N-alkylpyrazoles useful as an intermediate for medicines and agricultural chemicals at a high yield.
As a result of the present inventors' earnest study for satisfying the foregoing demand, it has been found that N-alkylpyrazoles represented by the formula (1) can be obtained at a high yield by reacting an alkali metal or an alkali metal-containing base with N-unsubstituted pyrazoles represented by the formula (2) to form an alkali metal salt thereof and, subsequently, reacting the obtained alkali metal salt of pyrazoles with alkylating agents. ##STR2## (wherein R.sup.1 represents a hydrogen atom or a C.sub.1 -C.sub.4 alkyl group, R.sup.2 represents a C.sub.1 -C.sub.4 alkyl group and n represents an integer of 1 to 3).
The present invention has been attained on the basis of the above-mentioned finding.